syllable
噔 is a rare kanji used phonetically to represent the syllable 'tou' or a similar sound, often in onomatopoeic or transliterated contexts. Its standalone meaning is unclear beyond this syllabic function.
噔 is a phono-semantic compound with 口 (mouth) suggesting a sound-related meaning and 登 providing the phonetic element. It was likely created to represent a specific syllable in transliterations or onomatopoeia.
The mouth radical 口 beside 登 suggests a vocal sound. Imagine a loud '噔' (tou) echoing as someone climbs (登) and shouts.
For トウ, picture a toe (トウ) tapping to the syllable sound: toe -> トウ, and the mouth 口 makes the 'tou' noise.